When moisture or gases collect in a roofing system, many problems can occur when the moisture or gases are trapped beneath the waterproof roofing membrane used to seal a roof. Different types of venting means have been used in attempts to find a satisfactory solution to this problem. Roofing vents, including roofing vents having one way valves, have been used in the past. Gases may particularly be found in a roofing system if polyurethane or polyisocyanurate roofing insulation is used.
The patent to Golde (U.S. Pat. No. 335,577) shows a shed construction including vent outlets. Patry (U.S. Pat. No. 3,984,947) describes a roof structure including a one-way vapor vent through which moist air within the structure passes to the ambient surroundings. Kelly (U.S. Pat. No. 4,223,486) describes a roof structure provided with one or more one-way valves, the base of each valve opening into an area between a loosely laid membrane and the roof between the loosely laid membrane and the insulation with the negative air pressure which occurs on the top of the roof when wind blows across the roof. The roof vent of the Logsdon patent (U.S. Pat. No. 4,484,424) is directed to a one-way vent which allows for passage of fluid from between the layers of the roof to the ambient, but does not show a roofing cant. The ventilated device of the Ballard patent (U.S. Pat. No. 4,538,508) allows escape of air from enclosed spaces through an insert which includes a flow control valve, but does not show a roofing cant.
Conventional roofing cants include triangularly cut wood strips, which have the disadvantage of being subject to warping and/or rotting.